I’ve got a lemon tree growing in a large pot at the back doorstep. It’s just bursting in to bloom at the moment. Unfortunately it is also starting to get a bit of scale appearing on the undersides of some of the leaves.
If you’ve got scale on your citrus trees, you’ll probably also notice that there are ants crawling over your tree too. Scales shoot a sweet substance called honeydew. Ants like to ‘farm’ the scale to feed on the honeydew. They’ll even pick the scale up and move them all over the tree. Honeydew also leads to sooty mould, a black dusty fungus that grows over the leaves and stems. Controlling the scale will also get rid of the sooty mould.
Scale in large numbers can cause leaf yellowing, leaf drop and die-back. Don’t worry though, it’s easily treated with a spray of white oil, which suffocates them. The great news is that it’s easy to make your own white oil to treat scale and aphids.
Different types of scale on citrus trees
There are many different types of scale that can affect citrus trees. Some only persist on the undersides of leaves. Others cover the fruit, causing little brown specks to appear all over the skin. Don’t worry and fruit affected with scale is perfectly fine to eat. The damage is only cosmetic.
Treat the underlying cause, rather than just the symptoms
You can reach for the white oil, to kill the scale. My approach to controlling scale is to treat the underlying root cause.
I have noticed that scale tend to present on trees that are struggling to obtain the nutrients that they need to grow strong and healthy. An underfed tree tends to attract scale. There are many different ways to top up soil nutrients for your citrus tree. A handful of general purpose organic fertilizer will usually do the trick. It will also help the tree to be more productive. In our citrus gall wasp experiment we found that fertilizing regimes had a huge influence in the productivity of the trees.
Want to know more?
I have written a 5 part guide to growing citrus. Check them out: